Adolescence is a time of rapid -- and often awkward and uncomfortable -- physical development. While many teens worry about gaining too much weight, a study published in the Journal of the American Dietetic Association in 2001 estimated that 17 percent to 37 percent of teenage males would like to bulk up. It's important to encourage healthy muscle building as your teen will probably be exposed to unhealthy temptations, including steroids and expensive supplements.
Encourage your teen to be realistic. If your son's parents and siblings are thin with a slight build, your teen is probably genetically predisposed to thinness. He can add muscle mass, but he isn't likely to achieve the bulk of a linebacker. Remind your teen that good health and overall fitness are far more important than appearance.
Make sure your teen eats enough protein. Contrary to what infomercials would have you believe, excessive protein consumption won't help build muscle. Any extra protein your son takes in will be burned or stored as fat, according to Nancy Clark of the American College of Sports Medicine journal. Still, your son needs to eat roughly 1.6 to 1.7 grams of protein per kilogram of weight. Offer lean meat, beans and low-fat dairy to help him meet his quota.
Balance carbohydrates with protein. Healthy, whole-grain carbohydrates are the fuel for exercise. If your teenager doesn't eat enough carbohydrates, protein will be used for energy instead of to build muscle. Encourage your teen to eat plenty of fruits, vegetables and whole-grain bread, pasta and cereal.
Help your teen design a workout program. Strength training is an excellent way to build muscle, strengthen tendons and prevent injury. It's important to differentiate between strength training and bodybuilding, however. A workout program for teenage boys should focus on low-weight, high-repetition exercises. Trying to bulk up with bodybuilding moves can be dangerous for an adolescent, according to the University of Rochester Medical Center. Write up a schedule of full-body exercises your teen can do with free weights or resistance bands several days each week. He should rest for 24 hours between sessions.
Don't forget aerobic exercise. Although not as useful for building muscle, cardiovascular exercise is essential for adolescent health. Encourage your teen to join a sports team or run, cycle or walk to keep his heart and lungs healthy.